α-Fe 2 O 3 nanosheet-assembled hierarchical hollow mesoporous microspheres: Microwave-assisted solvothermal synthesis and application in photocatalysis

Molybdenum-doped iron oxide nanostructures synthesized via a chemical co-precipitation route for efficient dye degradation and antimicrobial performance: in silico molecular docking studies

In this research, various concentrations of molybdenum (2, 4 and 6 wt%) doped Fe₃O₄ nanostructures (Mo-Fe₃O₄ NSs) were prepared via a co-precipitation technique. Various techniques were then used to investigate the optical, morphological and structural properties of the NSs in the presence of the dopant materials. X-ray diffraction (XRD) was used to investigate the crystalline nature of the prepared NSs and confirm the orthorhombic and tetragonal structure of Fe₃O₄, with a decrease in crystallinity and crystallite sizes of 36.11, 38.45, 25.74 and 24.38 nm with increasing concentration of Mo (2, 4 and 6%). Fourier-transform infrared (FTIR) spectroscopy analysis was carried out to examine the functional groups in the NSs. Structure, surface morphology and topography were examined via field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM), which confirmed the fabrication of nanoparticles and nanorods and a floccule-like morphology with a higher doping concentration and the interlayer d-spacing was calculated using high-resolution (HR)TEM, the results of which were a good match to the XRD data. The presence of Mo, Fe and O in a lattice of Mo (2, 4 and 6%) doped Fe₃O₄ was confirmed by energy dispersive X-ray spectroscopy (EDS) analysis. The energy band gap (E _g) was measured via the optical analysis of pure and doped samples, showing a decrease from 2.76 to 2.64 eV. The photoluminescence (PL) spectra exhibit a higher charge combination rate of electron-hole pairs with a higher concentration of doping. The NSs exhibited excellent catalytic activity (CA) in degrading methylene blue (MB) dye in a basic medium by around 86.25%. Additionally, the antimicrobial activity was tested against Escherichia coli (E. coli) bacteria. Pairs of electrons and holes are the fundamental basis for generating reactive oxygen species that kill bacteria. The significant inhibition zones were calculated against E. coli bacteria at around 3.45 mm compared to ciprofloxacin. In silico docking investigations of the Mo-Fe₃O₄ NSs for dihydropteroate synthase (DHPS, binding score: 6.16 kcal mol^-1), dihydrofolate reductase (DHFR, binding score: 6.01 kcal mol^-1), and β-ketoacyl-acyl carrier protein synthase III (FabH, binding score: 5.75 kcal mol^-1) of E. coli show the suppression of the aforementioned enzymes as a potential mechanism besides their microbicidal assay.

Green synthesis of graphite-based photo-Fenton nanocatalyst from waste tar via a self-reduction and solvent-free strategy

Thermochemical conversion of biomass yields large quantities of tar as a by-product, which is a potential precursor for the synthesis of renewable carbon-based functional materials. In this study, high-performance photo-Fenton catalyst of graphite‑carbon-supported iron nanoparticles was synthesized using a self-reduction and solvent-free approach. The results showed that the tar-derived catalyst had unique properties including a defect-rich graphitic structure, high surface area, and an abundant porous structure resulting from the inherent properties of biomass tar. The iron nanoparticles were highly dispersed within the prepared catalysts and were stably anchored on the carbonaceous surface by the FeC bond. The prepared nanocatalyst showed the highest decomposition constant (91.87 × 10^-3 min^-1) for 20 mM H₂O₂, and 40 mg/L RhB can be completely degraded within 2 h under catalyst dosage of 1 g/L and H₂O₂ addition of 20 mM. The degradation mechanism under the photo-Fenton catalyst/H₂O₂/light system included the heterogeneous Fenton reaction of iron nanoparticles and photo-Fenton reaction of iron oxide, and the efficient RhB degradation was mainly ascribed to the heterogeneous Fenton reaction. In addition, recycling and leaching tests demonstrated that the photo-Fenton catalyst had excellent reusability and stability, where only 7.3% catalytic reactivity was reduced after five cycles. This work provided a green, sustainable, and facile approach for synthesizing photo-Fenton catalysts by value-added utilization of tar wastes.

A synergistic strategy to remove hazardous water pollutants by mimicking burdock flower morphology structures of iron oxide phases

Artificially mimicking structures/morphologies available in the nature to develop multifunctional materials for catalysis is receiving greater attention. Particularly, the burdock flower morphology, which has a hollow-globe surrounded by spiky sheets, represents a multifunctional structure helpful in adsorption as well as intercalation of molecules. Given this, we have strategically developed a robust microwave (MW) bubble-template process to achieve highly uniform α-Fe₂O₃ and carbon-enriched Fe₃O₄ (Fe₃O₄@C) phases resembling the characteristics of spiky hollow burdock morphologies. The utilization of the MW bubble-templates as a pretreatment to the iron-based precursor solution helps in producing hollowed open-space ferrous glycolate burdock flower morphology with rapid production rate and without any addition of extra agents. Such burdock flower structures remain intact even after annealing in air/N₂ ambiance providing highly photoactive α-Fe₂O₃ or magnetic Fe₃O₄@C, respectively. Utilizing the hollow burdock flower structures together with the individual photo/magnetic properties of iron oxide phases, a dual-layer filter was designed to remove hazardous dye molecules from water, which efficiently photodegraded (99.2 %) in natural sunlight as well as showed excellent adsorption (99.7 %) within minutes. Comparatively, a lower catalytic activity using simple iron oxide nanoparticles, closed, and faded burdock morphologies were seen. Hence, the high catalytic activity in removing the dye molecules, retention of structural phases after repeated use, and strong durability were a result of the synergetic effect of photo/magnetic properties, activated surface/spiky open burdock structure.

Recent progress, synthesis, and applications of chitosan-decorated magnetic nanocomposites in remediation of dye-laden wastewaters

Over the past several decades, the disposal of dyes from the industrial manufacturing sector has had an inadvertent impact on water ecology as polluted water bodies with these hazardous dyes...

Heterogeneous activation of peroxymonosulfate by Co-doped Fe2O3 nanospheres for degradation of p-hydroxybenzoic acid

Environmental remediation has become more effective when using nanotechnologies. In this study, iron oxide (α-Fe₂O₃) nanospheres with different cobalt doping levels (xCo-Fe₂O₃) were synthesised and applied in the heterogeneous activation of peroxymonosulfate (PMS) for the degradation of p-hydroxybenzoic acid (p-HBA). The catalyst (3Co-Fe₂O₃) with 3% Co doping exhibits the best performance for PMS activation, possibly because of the larger specific surface area and the tailored catalyst surface as confirmed by X-ray photoelectron spectroscopy (XPS). Reaction parameters were investigated to optimise the degradation efficiency. The metal ions leaching tests confirmed the higher stability of the catalyst, thanks to the leaching suppression by the doping of Co²⁺. The main contribution of free radicals (SO₄^•- and ^•OH) was confirmed by electron paramagnetic resonance (EPR) spectra, whereas partial contribution of oxygen anions and singlet oxygen (O₂^•-, ¹O₂) was observed during the quenching tests. Finally, a radical based degradation mechanism was proposed for the removal of p-HBA. It is expected to open up a novel perspective for the application of iron oxide as a potential catalyst for the removal of emerging contaminants.

Fe-based Fenton-like catalysts for water treatment: Preparation, characterization and modification

Fenton reaction based on hydroxyl radicals () is effective for environment remediation. Nevertheless, the conventional Fenton reaction has several disadvantages, such as working at acidic pH, producing iron-containing sludge, and the difficulty in catalysts reuse. Fenton-like reaction using solid catalysts rather than Fe²⁺ has received increasing attention. To date, Fe-based catalysts have received increasing attention due to their earth abundance, good biocompatibility, comparatively low toxicity and ready availability, it is necessary to review the current status of Fenton-like catalysts. In this review, the recent advances in Fe-based Fenton-like catalysts were systematically analyzed and summarized. Firstly, the various preparation methods were introduced, including template-free methods (precipitation, sol gel, impregnation, hydrothermal, thermal, and others) and template-based methods (hard-templating method and soft-templating method); then, the characterization techniques for Fe-based catalysts were summarized, such as X-ray diffraction (XRD), Brunauer, Emmett and Teller (BET), SEM (scanning electron microscopy)/TEM (transmission electron microscopy)/HRTEM (high-resolution TEM), FTIR (Fourier transform infrared spectroscopy)/Raman, XPS (X-ray photoelectron spectroscopy), ⁵⁷Fe Mössbauer spectroscopy etc.; thirdly, some important conventional Fe-based catalysts were introduced, including iron oxides and oxyhydroxides, zero-valent iron (ZVI) and iron disulfide and oxychloride; fourthly, the modification strategies of Fe-based catalysts were discussed, such as microstructure controlling, introduction of support materials, construction of core-shell structure and incorporation of new metal-containing component; Finally, concluding remarks were given and the future perspectives for further study were discussed. This review will provide important information to further advance the development and application of Fe-based catalysts for water treatment.

Facile synthesis of nanosheet-assembled γ-Fe2O3 magnetic microspheres and enhanced Sb(III) removal

The development and utilization of magnetic nanoadsorption materials with large adsorption capacity and easy separation are the research hotspot nowadays. In this study, nanosheet-assembled maghemite (γ-Fe₂O₃) magnetic microspheres were successfully synthesized by an environmental friendly, quick, and simple method, for enhanced Sb(III) removal from aqueous solution. Scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometer (VSM), and Brunauer-Emmett-Teller (BET) were used to characterize the material. The results showed that the product contained flower-like γ-Fe₂O₃ microspheres composed of petal-shaped nanosheets interspersed with each other. The specific surface area and pore volume were 69.23 m²/g and 0.15 cm³/g, respectively. The material has a strong magnetic response, which allows rapid solid-liquid separation under the action of an external magnetic field. The effects of different dosages, solution pH, and contact time on the adsorption effect were studied by batch adsorption experiments, and the reusability of the materials was evaluated. Both Freundlich isothermal adsorption model and pseudo-second-order kinetic model were able to describe the uptake of Sb(III). The maximum adsorption capacity of the material was 47.48 mg/g under optimal conditions. The adsorption mechanism is mainly that Sb and lattice oxygen (O_X^2-) form Fe-O-Sb coordination bonds, which is incorporated into the crystal structure of γ-Fe₂O₃ as inner-sphere surface complexes. The synthetic material has the advantage of simple preparation process, good adsorption capacity, operation over a wide range of pH, and easy physical separation from treatment systems with good potential for future application to treat polluted wastewater.

Liquid-Phase Synthesis of Iron Oxide Nanostructured Materials and Their Applications

Owing to their high natural abundance, low cost, easy availability, and excellent magnetic properties, considerable interest has been devoted to the synthesis and applications of iron oxide nanostructured materials. Liquid-phase synthesis methods are economical and environmentally friendly with low energy consumption and volatile emissions, and as such have received much attention for the preparation of iron oxide nanostructured materials. Herein, the liquid-phase synthesis methods of iron oxide nanostructured materials including the co-precipitation method, microemulsion method, conventional hydrothermal and solvothermal methods, microwave-assisted heating method, sonolysis method, and other methods are summarized and reviewed. Many iron oxide nanostructured materials, self-assembled nanostructures, and nanocomposites have been successfully prepared, which are of great significance to enhance their structure-dependent properties and applications. The specific roles of liquid-phase chemical reaction parameters in regulating the chemical composition, structure, crystallinity, morphology, particle size, and dispersive behavior of the as-prepared iron oxide nanostructured materials are emphasized. The biomedical, environmental, and electrochemical energy storage applications of iron oxide nanostructured materials are discussed. Finally, challenges and perspectives are proposed for future investigations on the liquid-phase synthesis and applications of iron oxide nanostructured materials.

Photocatalytic defluorination of perfluorooctanoic acid by surface defective BiOCl: Fast microwave solvothermal synthesis and photocatalytic mechanisms

There is an urgent need for developing cost-effective methods for the treatment of perfluorooctanoic acid (PFOA) due to its global emergence and potential risks. In this study, taking surface-defective BiOCl as an example, a strategy of surface oxygen vacancy modulation was used to promote the photocatalytic defluorination efficiency of PFOA under simulated sunlight irradiation. The defective BiOCl was fabricated by a fast microwave solvothermal method, which was found to induce more surface oxygen vacancies than conventional solvothermal and precipitation methods. As a result, the as-prepared BiOCl showed significantly enhanced defluorination efficiency, which was 2.7 and 33.8 times higher than that of BiOCl fabricated by conventional solvothermal and precipitation methods, respectively. Mechanistic studies indicated that the defluorination of PFOA follows a direct hole (h⁺) oxidation pathway with the aid of •OH, while the oxygen vacancies not only promote charge separation but also facilitate the intimate contact between the photocatalyst surface and PFOA by coordinating with its terminal carboxylate group in a bidentate or bridging mode. This work will provide a general strategy of oxygen vacancy modulation by microwave-assisted methods for efficient photocatalytic defluorination of PFOA in the environment using sunlight as the energy source.

Preparation of reduced graphene oxide nanosheet/FexOy/nitrogen-doped carbon layer aerogel as photo-Fenton catalyst with enhanced degradation activity and reusability

In this manuscript, a novel reduced graphene oxide nanosheet/Fe_xO_y/nitrogen-doped carbon layer (rGS/Fe_xO_y/NCL) aerogel with Fe_xO_y NPs sandwiched between rGS and NCL was prepared via a two-step method. Their catalytic performance was evaluated in a photo-Fenton degradation of rhodamine B. It was found that rGS/Fe_xO_y/NCL aerogel represented higher degradation activity than the sum of rGS/NCL support and Fe_xO_y NPs, suggesting synergistic effect was established between support and reactive species. The degradation activity was investigated on the basis of aerogel usage, Fe_xO_y loading, H₂O₂ dosage, pH value and RhB concentration. To test stability and reusability, leaching experiments, cyclic experiments and structural analysis were carried out. Based on inhibitor experiment and intermediate detection, a possible catalytic mechanism and degradation pathway of RhB were proposed.

Photocatalytic properties of hierarchical CuO nanosheets synthesized by a solution phase method

CuO nanomaterials were synthesized by a simple solution phase method using cetyltrimethylammonium bromide (CTAB) as a surfactant and their photocatalytic property was determined towards the visible-light assisted degradation of Reactive Black-5 dye. A detailed mechanism for the formation of CuO nanostructures has been proposed. The effect of various experimental parameters such as catalyst amount, dye concentration, pH and oxidizing agent on the dye degradation efficiency was studied. About 87% dye was degraded at pH2 in the presence of CuO nanosheets under visible light. The enhanced photocatalytic activity of CuO nanosheets can be ascribed to good crystallinity, grain size, surface morphology and a strong absorption in the visible region. CuO is found to be a promising catalyst for industrial waste water treatment.

Fabrication and characterization of novel iodine doped hollow and mesoporous hematite (Fe2O3) particles derived from sol-gel method and their photocatalytic performances

In this work, iodine (I) doped hollow and mesoporous Fe₂O₃ photocatalyst particles were fabricated for the first time through sol-gel method. Phase structure, surface morphology, particle size, specific surface area and optical band gap of the synthesized Fe₂O₃ photocatalysts were analyzed by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), X-ray photoelectron spectroscopy (XPS), BET surface analysis, particle size analyzer and UV-vis diffuse reflectance spectrum (UV-vis DRS), respectively. Also, electrochemical properties and photoluminescence spectra of Fe₂O₃ particles were measured. The results illustrated that high crystalline, hollow and mesoporous Fe₂O₃ particles were formed. The optical band gap values of the Fe₂O₃ photocatalysts changed between 2.104 and 1.93eV. Photocatalytic efficiency of Fe₂O₃ photocatalysts were assessed via MB solution. The photocatalytic activity results exhibited that I doping enhanced the photocatalytic efficiency. 1% mole iodine doped (I-2) Fe₂O₃ photocatalyst had 97.723% photodegradation rate and 8.638×10^-2min^-1 kinetic constant which showed the highest photocatalytic activity within 45min. Moreover, stability and reusability experiments of Fe₂O₃ photocatalysts were carried out. The Fe₂O₃ photocatalysts showed outstanding stability after four sequence tests. As a result, I doped Fe₂O₃ is a good candidate for photocatalysts.

Fast interfacial charge transfer in α-Fe2O3-δCδ/FeVO4-x+δCx-δ@C bulk heterojunctions with controllable phase content

The novelties in this paper are embodied in the fast interfacial charge transfer in α-Fe₂O_3−δC_δ/FeVO_4−x+δC_x−δ@C bulk heterojunctions with controllable phase compositions. The carbon source-glucose plays an important role as the connecting bridge between the micelles in the solution, forming interfacial C-O, C-O-Fe and O-Fe-C bonds through dehydration and polymerization reactions. Then the extra VO₃⁻ around the FeVO₄ colloidal particles can react with unstable Fe(OH)₃, resulting the phase transformation from α-Fe₂O₃ (47.99–7.16%) into FeVO₄ (52.01–92.84%), promoting photocarriers’ generation capacities. After final carbonization, a part of C atoms enter into lattices of α-Fe₂O₃ and FeVO₄, forming impurity levels and oxygen vacancies to increase effective light absorptions. Another part of C sources turn into interfacial carbon layers to bring fast charge transfer by decreasing the charge transition resistance (from 53.15 kΩ into 8.29 kΩ) and the surface recombination rate (from 64.07% into 7.59%). The results show that the bulk heterojunction with 90.29% FeVO₄ and 9.71% α-Fe₂O₃ shows ideal light absorption, carriers’ transfer efficiency and available photocatalytic property. In general, the synergistic effect of optimized heterojunction structure, carbon replacing and the interface carbon layers are critical to develop great potential in stable and recoverable use.

Hierarchical photocatalysts

The design, fabrication, performance and applications of hierarchical semiconductor photocatalysts are thoroughly reviewed and apprised.

A controlled, template-free, and hydrothermal synthesis route to sphere-like α-Fe2O3 nanostructures for textile dye removal

Iron carbonate nanospheres were synthesized via hydrothermal treatment of aqueous solutions of iron sulfate, ascorbic acid and ammonium carbonate with a molar ratio of 1 : 1 : 3, respectively, at 140 °C for 1.5 h.

The formation mechanism of a Er3+-doped heterojunction ms/tz-BiVO4 with enhanced photocatalytic performance under visible light

The formation mechanism of Er³⁺ doped heterojunction BiVO₄ and enhanced photocatalysis.